1. Field of the Invention
The present invention relates to photographic cameras, and more particularly, to apparatus for determining optimum operation of adjustable camera mechanisms based on measured scene parameters.
2. Description Relative to the Prior Art
For every photograph made with a camera having adjustable mechanisms, a decision must be made, either by the camera designer or the photographer (or both), as to the adjustments that will provide an optimum quality picture. In the past, generally defined guidelines have determined what combinations of, say, aperture size, exposure time, flash energy output, and lens focus position would be used for each picture.
As an example, consider a photographic situation in which a group of people (photographic subjects) are seated around a table in a room. Assume that the photographer is equipped with a camera having adjustable shutter speed, aperture size, focus position, and variable flash output. The photographer is faced with a perplexing range of choices in taking the picture. One possible choice would be a hand-held "existing light" exposure. Generally, for such an exposure, the photographer chooses the maximum aperture size of which the camera is capable, and hence the minimum shutter time consistent with nominal exposure. These camera adjustments result in the minimum degradation to the picture due to camera shake, which under the circumstances, may still be appreciable. The depth of focus is minimized by the large aperture and it is therefore possible that there will be no single focus position at which all of the people in the scene are in focus. Consequently, the photographer may wish to select a compromise focus position that places best focus somewhere between the nearest subject and the more distant subjects. Both foreground and background subjects will be equally well (or poorly) focused.
Alternatively, the photographer may choose to employ flash illumination to take the picture. In this case, the photographer might select the minimum aperture size consistent with the maximum output of the flash device. The shutter speed will be the minimum required to synchronize the flash output with an open shutter. Degradation of the picture due to camera shake is virtually eliminated, and due to the small aperture, the depth of focus is generally improved over the "existing light" exposure. Unfortunately, a large variation in exposure between the foreground and the background may result because the flash illumination diminishes in proportion to the square of the distance from the flash device.
Faced with the above choices, the enlightened photographer may want to compromise between "existing light" and flash exposure to achieve a more nearly optimum quality photograph. If so, he would want to select an aperture size and shutter time which together would result in a certain amount of underexposure, and would want to supplement the exposure with a certain amount of flash illumination to improve the exposure as much as possible. Perhaps he would want to slightly overexpose the closest subjects to improve the exposure of subjects farther away, in which case, he would choose a shutter time and aperture combination that would optimally compromise between camera shake and depth of field. He may also want to choose a lens extension that would give an optimum balance between the sharpness of the nearest and farthest subjects.
A skilled photographer with a thorough knowledge of his equipment and knowledge of the general principles of photography may be able to select a camera adjustment, based on his knowledge, intuition and experience, that would result in a nearly optimum compromise. Heretofore, however, such performance has been beyond the reach of the average photographer. Short of trial and error, a systematic means has not been available, even to the skilled professional, for determining the camera adjustment which will result in an optimum quality photograph. Even in the most advanced, fully automatic cameras of the prior art, automatic control apparatus has not been provided for effecting the various compromises between camera settings that result in a picture of optimized overall quality. This problem is particularly apparent in highly automatic "instant" cameras. Cameras presently on the market provide automatic exposure control and automatic focusing. Automatic focusing is a desirable feature, because the quality of many amateur photographs taken by cameras which employ manual focusing is degraded due to focus error. Since the exposure latitude of instant film is very narrow, correct exposure is critical to an acceptable picture. One of the biggest problems in this area has been the control of exposure when a flash device is employed to supplement the illumination of the scene.
One highly automatic camera, typical of the state of the art, is shown in U.S. Pat. No. 3,917,395, issued Nov. 4, 1975 to F. T. Ogawa. Ogawa discloses a camera featuring automatically controlled focus, exposure, and flash output. The control circuit of the camera is responsive to a number of measured scene parameters to control the automatic functions. The lens extension is set to provide best focus at a distance determined by an automatic range finder. The maximum effective aperture and shutter time for each exposure are determined in response to measured scene light.
FIGS. 1a and b of the present application show, qualitatively, the exposure control program of this prior art automatic control system. As shown in FIG. 1a, the control system provides progressively larger apertures and longer shutter times for progressively lower light levels until a point is reached where the flash is enabled. The flash device provides a constant output of light, and exposure is controlled during flash operation by adjusting the aperture (and consequently the shutter speed, due to the mechanical design of the aperture/ shutter) as a function of distance as shown in FIG. 1b. As can be seen from FIGS. 1a and b, this prior art control system, although highly automated, does not effect a compromise between aperture size and shutter speed as a function of subject distance nor does it provide for a compromise between the quantity of flash exposure versus ambient exposure as a function of scene brightness and/or subject distance. The system does not provide the possibility of compromising exposure for sharpness. The automatic focusing feature does not allow for a lens extension that produces a best focus that compromises between the sharpness of the near subject and the sharpness of the background.
Accordingly, there is still a need for an automatic camera control apparatus capable of effecting the abovenoted compromises so that an optimum overall quality photograph may be achieved.